I thought the jurassic park series would end after part 3 but i heard Steven speilburg is currently writing the script for part 4.The script which has been on web is a fake as told by sam neil.John hammonds character is also being replaced by a new actor.
Moriarty over at Aint It Cool posted a script review a long time ago and if it's true and gets made it will be a major departure from the other three. Sounds pretty wacked out to me, but in the right hands it might work. I know a few of the opinions around here about genetically produced weapons(maybe someone slipped him the Raptor Island sequel script).
JP4 script review (http://www.aintitcool.com/display.cgi?id=18166)
They should end with 3, when you have a good sequel stop while you're ahead.